I reported earlier that after buying ($28 USD each) the Shuguang Preferred Series 274B series rectifier (above and below), I found that its oversize bottle was too big to fit in the Fi 300B monos, so I’ve really been looking forward to hearing them in my Sophia Electric 91-01 mono amps which have no size restrictions like the Fi 300B monos do. You can use an ST-16 size bulb in the Fi, but anything bigger than that will not fit.

So consider this a first impression with no time on the 274Bs to speak of – so they’re not broken in at all – and I haven’t done any comparative listening with the vintage JAN 5Z3PA (below) that Sue at Sophia Electric sent me yet (which is a tube that I really love). With those caveats in mind, let me just say that I really like what I’m hearing from the 274B rectifier in the 91-01 amps, and at $28 per rectifier the price is right.

More to come as I get some time on the 274B rectifiers and I have time to compare them to the vintage 5Z3PA.

UPDATE!I got a message from Sue at Sophia Electric warning against using the 274B rectifier in the Sophia Electric 91-01 300B mono amplifiers. Here’s Sue’s message:

Hi Jeff,

I very much enjoy your latest blog and would like to contribute some supplementary information for your reference.

Sophia Electric 91-01 amplifiers use 22uf value for the first capacitor in the power supply. That is smaller than the industry popular use of 47uf. However, to use 274B for long term, WE requires the first cap after 274B to be 4uf or smaller. Sophia Electric 274B requires the cap to no larger than 8uf to achieve long term use. 22uf may work in most situations, however, it may shorten the 274B lifespan (like cigarette is harmful for health) and pose danger to the amplifier (occasionally, it can blow out fuses or caps if not follow the rule). Thus, Sophia Electric would not recommend to use any 274B in Sophia Electric 91-01 amplifiers. The long term the most reliable, the most beautiful sounding and the most cost efficient choice is the NOS rectifier supplied by Sophia Electric and recommended by Jeff Day in his previous blogs.

Best regards,

Sue

So there you have it, ixnay on the 274B rectifier in the Sophia Electric 91-01, so I’ll be sticking with the rectifiers Sophia Electric recommends. It’s one of those fortunate situations: the 274B works fine in the Fi 300B mono amplifiers electrically, but because of its oversize ST bottle shape, in will not fit in the chassis cutout of the Fi, which will only accept up to an ST-16 bottle size (the bottle used in NOS RCA, Tung Sol, and so forth). So if any of you have amps that are compatible with the 274B be sure to let me know how it sounds, as my first impressions here were very positive, but I don’t want to risk damaging my beloved Sophia 91-01 amps, so the 274B rectifiers will be retired from service until something compatible comes along.

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Well that’s a bummer! I was really excited to give the 274B’s a shot. I have my own RCA coke-bottle shapped NOS tubes, but was quite curious about these. Oh well… I guess I shouldn’t be surprised these days.

I know what you mean, I was really disappointed to find that out too. You can run almost anything in the Fi 300B mono amps, and I thought I remembered it was the same for the Sophia’s, but it appears not to be so.

I love my Sophia’s too! They were’s really sounding great on the Kingdom Royals last night!

Hi Jeff Has anybody tried the Sophia 91-01 with the Tannoy Canterbury SE’s? I bought a pair after conversing with Jim Smith and I need an amp. I’m considering the deHavilland Aries and the Sophia 91-01 but I want to be sure I have enough power. The Caterburys are 96db vs. the 99 db. of the Westies, so these 2 amps might not cut it power wise. I’m in the timbral camp as far as listening bias goes and want that sweet tube flavor but also need some punch to go with it when called for. I simply play a Barney Kessel album to see if the prospective component has the guitar bass and drums sound the way I heard it live when I knew Barney and then follow it up with ZZ Top. If it can do both, it’s a winner to me. Thanks, Billy